Conventionally-known detection apparatuses include, for example, detection apparatuses described in U.S. Pat. No. 7,652,952, which discloses a side scan sonar functioning based on pulsed transmission. One difficulty encountered with such technology is that the refresh rate is slow, which creates zones that cannot be detected if the ship exceeds a certain speed. With a side scan sonar functioning based on pulsed transmission, it is often recommended by manufacturers that a boat speed be kept below 7 knots (kn) to avoid missing underwater targets. However, a ship speed may often exceed 30 kn, therefore the ship is required to slow down in order to accurately use the sonar system. This limitation has constrained the practical application of side scan sonar technology in boats and ships that travel at faster speeds.
A synthetic aperture side scan sonar is disclosed in EP0199571, for example. Synthetic aperture side scan sonar technology synthesizes multiple reception signals for each line in an image. However, the processing power required increases manufacturing costs and complexity for such devices.